This invention relates to sensor systems in which optical sensing systems are used.
Electro-mechanical resonating transducers are used as strain sensors in a variety of applications. Typically such a device comprises an oscillation system which is maintained in a state of oscillation by a feedback arrangement. The use of optical sensing systems in such devices is advantageous in that it reduces losses due to the feedback system.
One system in which optical techniques are used is described in British Patent Specification No. 2121953A (ITT Industries) to which corresponds U.S. Pat. No. 4,567,451 (J. C. Greenwood). In this, a transducer has an electrically supported paddle, typically of silicon, driven electrostatically at its natural frequency, or an harmonic thereof, by voltage pulses applied to an adjacent electrode. These pulses are derived from optical pulses fed via an optical fiber and reflected from the paddle on to a photo-diode array. The paddle's oscillators are sensed, also via the optical fiber, and used to control the formation of the optical pulses. Thus there is minimal coupling between the paddle and the drive sensing system.
Other systems using optical sensing techniques are described in U.S. Pat. No. 4,345,482 (Adolfsson et al) and U.S. Pat. No. 4,379,226 (Sichting et al).
An object of our invention is to produce a sensing arrangement which is superior to those described in the above mentioned documents.